8-speed transmission

ABSTRACT

The transmission has a plurality of members that can be utilized in powertrains to provide eight forward speed ratios and one reverse speed ratio. The transmission includes four planetary gear sets having five torque-transmitting mechanisms, two fixed interconnections and one grounded member. The powertrain includes an engine and torque converter that is continuously connected to at least one of the planetary gear members and an output member that is continuously connected with another one of the planetary gear members. The five torque-transmitting mechanisms provide interconnections between various gear members, and the transmission housing, and are operated in combinations of two to establish at least eight forward speed ratios and at least one reverse speed ratio.

TECHNICAL FIELD

The present invention relates to a power transmission having fourplanetary gear sets that are controlled by five torque-transmittingdevices to provide eight forward speed ratios and one reverse speedratio.

BACKGROUND OF THE INVENTION

Passenger vehicles include a powertrain that is comprised of an engine,multi-speed transmission, and a differential or final drive. Themulti-speed transmission increases the overall operating range of thevehicle by permitting the engine to operate through its torque range anumber of times. The number of forward speed ratios that are availablein the transmission determines the number of times the engine torquerange is repeated. Early automatic transmissions had two speed ranges.This severely limited the overall speed range of the vehicle andtherefore required a relatively large engine that could produce a widespeed and torque range. This resulted in the engine operating at aspecific fuel consumption point during cruising, other than the mostefficient point. Therefore, manually-shifted (countershafttransmissions) were the most popular.

With the advent of three- and four-speed automatic transmissions, theautomatic shifting (planetary gear) transmission increased in popularitywith the motoring public. These transmissions improved the operatingperformance and fuel economy of the vehicle. The increased number ofspeed ratios reduces the step size between ratios and therefore improvesthe shift quality of the transmission by making the ratio interchangessubstantially imperceptible to the operator under normal vehicleacceleration.

Six-speed transmissions offer several advantages over four- andfive-speed transmissions, including improved vehicle acceleration andimproved fuel economy. While many trucks employ power transmissionshaving six or more forward speed ratios, passenger cars are stillmanufactured with three- and four-speed automatic transmissions andrelatively few five or six-speed devices due to the size and complexityof these transmissions.

Seven-, eight- and nine-speed transmissions provide further improvementsin acceleration and fuel economy over six-speed transmissions. However,like the six-speed transmissions discussed above, the development ofseven-, eight- and nine-speed transmissions has been precluded becauseof complexity, size and cost.

SUMMARY OF THE INVENTION

The present invention provides an improved transmission having fourplanetary gear sets controlled to provide at least eight forward speedratios and at least one reverse speed ratio.

The transmission family of the present invention has four planetary gearsets, each of which includes a first, second and third member, whichmembers may comprise a sun gear, a ring gear, or a planet carrierassembly member, in any order.

In referring to the first, second, third and fourth gear sets in thisdescription and in the claims, these sets may be counted “first” to“fourth” in any order in the drawing (i.e., left to right, right toleft, etc.). Additionally, the first, second or third members of eachgear set may be counted “first” to “third” in any order in the drawing(i.e., top to bottom, bottom to top, etc.) for each gear set.

Each carrier member can be either a single-pinion carrier member(simple) or a double-pinion carrier member (compound). Embodiments withlong pinions are also possible.

A first interconnecting member continuously connects the third member ofthe first planetary gear set with the first member of the secondplanetary gear set, with the third member of the third planetary gearset and with the second member of the fourth planetary gear set.

A second interconnecting member continuously connects the second memberof the first planetary gear set with the second member of the secondplanetary gear set.

The input member is continuously connected with the first member of thethird planetary gear set. The output member is continuously connectedwith the third member of the fourth planetary gear set.

The first member of the first planetary gear set is continuouslyconnected with a stationary member (transmission housing/casing).

A first torque-transmitting device, such as a brake, selectivelyconnects the second member of the third planetary gear set with astationary member (transmission housing/casing).

A second torque-transmitting device, such as a clutch, selectivelyconnects the second member of the first planetary gear set with thefirst member of the third planetary gear set.

A third torque-transmitting device, such as a clutch, selectivelyconnects the third member of the second planetary gear set with thefirst member of the fourth planetary gear set.

A fourth torque-transmitting device, such as a clutch, selectivelyconnects the first member of the third planetary gear set with the firstmember of the fourth planetary gear set.

A fifth torque-transmitting device selectively connecting said secondmember of the third planetary gear set with the first member of thefourth planetary gear set.

The five torque-transmitting devices are selectively engageable incombinations of two to yield at least eight forward speed ratios and atleast one reverse speed ratio. Each shift is a single transition shiftand a quadruple overdrive is provided.

A variety of speed ratios and ratio spreads can be realized by suitablyselecting the tooth ratios of the planetary gear sets.

The above features and other features and advantages of the presentinvention are readily apparent from the following detailed descriptionof the best modes for carrying out the invention when taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic representation of a powertrain including aplanetary transmission in accordance with the present invention;

FIG. 1 b is a truth table and chart depicting some of the operatingcharacteristics of the powertrain shown in FIG. 1 a; and

FIG. 1 c is a schematic representation of the powertrain of FIG. 1 adepicted in lever diagram form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings, there is shown in FIG. 1 a a powertrain 10having a conventional engine and torque converter 12, a planetarytransmission 14, and a conventional final drive mechanism 16. The engine12 may be powered using various types of fuel to improve the efficiencyand fuel economy of a particular application. Such fuels may include,for example, gasoline; diesel; ethanol; dimethyl ether; etc.

The planetary transmission 14 includes an input member 17 continuouslyconnected with the engine 12, a planetary gear arrangement 18, and anoutput member 19 continuously connected with the final drive mechanism16. The planetary gear arrangement 18 includes four planetary gear sets20, 30, 40 and 50.

The planetary gear set 20 includes a sun gear member 22, a ring gearmember 24, and a planet carrier assembly member 26. The planet carrierassembly member 26 includes a plurality of pinion gears 27 rotatablymounted on a carrier member 29 and disposed in meshing relationship withboth the ring gear member 24 and the sun gear member 22.

The planetary gear set 30 includes a sun gear member 32, a ring gearmember 34, and a planet carrier assembly member 36. The planet carrierassembly member 36 includes a plurality of pinion gears 37 mounted on acarrier member 39 and disposed in meshing relationship with both thering gear member 34 and the sun gear member 32.

The planetary gear set 40 includes a sun gear member 42, a ring gearmember 44, and a planet carrier assembly member 46. The planet carrierassembly member 46 includes a plurality of pinion gears 47, 48 rotatablymounted on a carrier member 49. The pinion gears 47 are disposed inmeshing relationship with the sun gear member 42, and the pinion gears48 are disposed in meshing relationship with both the ring gear member44 and the respective pinion gear 47.

The planetary gear set 50 includes a sun gear member 52, a ring gearmember 54, and a planet carrier assembly member 56. The planet carrierassembly member 56 includes a plurality of pinion gears 57 mounted on acarrier member 59 and disposed in meshing relationship with both thering gear member 54 and the sun gear member 52.

The planetary gear arrangement also includes five torque-transmittingdevices 80, 82, 84, 85 and 86. The torque-transmitting device 80 is astationary type torque-transmitting mechanism, commonly termed brake orreaction clutch. The torque-transmitting devices 82, 84, 85 and 86 arerotating-type torque-transmitting mechanisms, commonly termed clutches.

The input member 17 is continuously connected with the sun gear member42 of the planetary gear set 40. The output member 19 is continuouslyconnected with the ring gear member 54 of the planetary gear set 50.

The sun gear member 22 of the planetary gear set 20 is continuouslyconnected with the transmission housing 60.

A first interconnecting member 70 continuously connects the ring gearmember 24 of the planetary gear set 20 with the sun gear member 32 ofthe planetary gear set 30, the ring gear member 44 of the planetary gearset 40 and the planet carrier assembly member 56 of the planetary gearset 50. A second interconnecting member 72 continuously connects theplanet carrier assembly member 26 of the planetary gear set 20 with theplanet carrier assembly member 36 of the planetary gear set 30.

A first torque-transmitting device, such as brake 80, selectivelyconnects the planet carrier assembly member 46 of the planetary gear set40 with the transmission housing 60. A second torque-transmittingdevice, such as clutch 82, selectively connects the planet carrierassembly member 26 of the planetary gear set 20 and the planet carrierassembly member 36 of the planetary gear set 30 via interconnectingmember 72 with the sun gear member 42 of the planetary gear set 40. Athird torque-transmitting device, such as clutch 84, selectivelyconnects the ring gear member 34 of the planetary gear set 30 with thesun gear member 52 of the planetary gear set 50. A fourthtorque-transmitting device, such as clutch 85, selectively connects thesun gear member 42 of the planetary gear set 40 with the sun gear member52 of the planetary gear set 50. A fifth torque-transmitting device,such as clutch 86, selectively connects the planet carrier assemblymember 46 of the planetary gear set 40 with the sun gear member 52 ofthe planetary gear set 50.

As shown in FIG. 1 b, and in particular the truth table disclosedtherein, the torque-transmitting mechanisms are selectively engaged incombinations of two to provide at least eight forward speed ratios andat least one reverse speed ratio, all with single transition shifts.

As set forth above, the engagement schedule for the torque-transmittingmechanisms is shown in the truth table of FIG. 1 b. The chart of FIG. 1b describes the ratio steps that are attained in the above describedtransmission. For example, the step ratio between the first and secondforward speed ratios is 1.41, while the step ratio between the reversespeed ratio and first forward ratio is −0.87.

Referring to FIG. 1 c, the embodiment of powertrain 10 depicted in FIG.1 a is illustrated in a lever diagram format. A lever diagram is aschematic representation of the components of a mechanical device suchas an automatic transmission. Each individual lever represents aplanetary gearset, wherein the three basic mechanical components of theplanetary gear are each represented by a node. Therefore, a single levercontains three nodes: one for the sun gear member, one for the planetgear carrier member, and one for the ring gear member. The relativelength between the nodes of each lever can be used to represent thering-to-sun ratio of each respective gearset. These lever ratios, inturn, are used to vary the gear ratios of the transmission in order toachieve appropriate ratios and ratio progression. Mechanical couplingsor interconnections between the nodes of the various planetary gear setsare illustrated by thin, horizontal lines and torque transmittingdevices such as clutches and brakes are presented as interleavedfingers. If the device is a brake, one set of the fingers is grounded.Further explanation of the format, purpose and use of lever diagrams canbe found in SAE Paper 810102, authored by Benford, Howard and Leising,Maurice, “The Lever Analogy: A New Tool in Transmission Analysis”, 1981,which is hereby fully incorporated by reference.

The powertrain 10 includes an input member 17, an output member 19, afirst planetary gear set 20A having three nodes: a first node 22A, asecond node 26A and a third node 24A; a second planetary gear set 30Ahaving three nodes: a first node 32A, a second node 36A and a third node34A; a third planetary gear set 40A having three nodes: a first node42A, a second node 46A and a third node 44A; and a fourth planetary gearset 50A having three nodes: a first node 52A, a second node 56A and athird node 54A.

The input member 17 is continuously connected with node 42A. The outputmember 19 is continuously connected with the node 54A.

The node 22A is continuously connected with the transmission housing 60.

The nodes 24A, 32A, 44A and 56A are continuously connected viainterconnecting member 70. The node 26A is continuously connected withnode 36A via interconnecting member 72.

A first torque-transmitting device, such as brake 80, selectivelyconnects the node 46A with the transmission housing 60. A secondtorque-transmitting device, such as clutch 82, selectively connects thenode 26A and node 36A via interconnecting member 72 with the node 42A. Athird torque-transmitting device, such as clutch 84, selectivelyconnects the node 34A with the node 52A. A fourth torque-transmittingdevice, such as clutch 85, selectively connects the node 42A with thenode 52A. A fifth torque-transmitting device, such as clutch 86,selectively connects the node 46A with the node 52A.

To establish ratios, two torque-transmitting devices are engaged foreach gear state. The engaged torque-transmitting devices are representedby an “X” in each respective row in FIG. 1 b. For example, to establishreverse gear, the brake 80 and clutch 85 are engaged. The brake 80engages the node 46A with the transmission housing 60. The clutch 85engages the node 42A with the node 52A. Likewise, the eight forwardspeed ratios are achieved through different combinations of clutchengagement as per FIG. 1 b.

The powertrain 10 may share components with a hybrid vehicle, and such acombination may be operable in a “charge-depleting mode”. For purposesof the present invention, a “charge-depleting mode” is a mode whereinthe vehicle is powered primarily by an electric motor/generator suchthat a battery is depleted or nearly depleted when the vehicle reachesits destination. In other words, during the charge-depleting mode, theengine 12 is only operated to the extent necessary to ensure that thebattery is not depleted before the destination is reached. Aconventional hybrid vehicle operates in a “charge-sustaining mode”,wherein if the battery charge level drops below a predetermined level(e.g., 25%) the engine is automatically run to recharge the battery.Therefore, by operating in a charge-depleting mode, the hybrid vehiclecan conserve some or all of the fuel that would otherwise be expended tomaintain the 25% battery charge level in a conventional hybrid vehicle.It should be appreciated that a hybrid vehicle powertrain is preferablyonly operated in the charge-depleting mode if the battery can berecharged after the destination is reached by plugging it into an energysource.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A multi-speed transmission comprising: an input member; an outputmember; first, second, third and fourth planetary gear sets each havingfirst, second and third members; a first interconnecting membercontinuously connecting said third member of the first planetary gearset with the first member of the second planetary gear set, the thirdmember of the third planetary gear set and the second member of thefourth planetary gear set; a second interconnecting member continuouslyconnecting said second member of the first planetary gear set with thesecond member of the second planetary gear set; said first member ofsaid first planetary gear set being continuously connected with astationary member; and five torque-transmitting devices for selectivelyinterconnecting said members of said planetary gear sets with saidstationary member or with other members of said planetary gear sets,said five torque-transmitting devices being engaged in combinations oftwo to establish at least eight forward speed ratios and at least onereverse speed ratio between said input member and said output member. 2.The transmission of claim 1, wherein a first of said five torquetransmitting devices is operable for selectively connecting said secondmember of said third planetary gear set with said stationary member. 3.The transmission of claim 2, wherein a second of said five torquetransmitting devices is operable for selectively connecting said secondmember of said first planetary gear set with said first member of saidthird planetary gear set.
 4. The transmission of claim 3, wherein athird of said five torque transmitting devices is operable forselectively connecting said third member of said second planetary gearset with said first member of said fourth planetary gear set.
 5. Thetransmission of claim 4, wherein a fourth of said five torquetransmitting devices is operable for selectively connecting said firstmember of said third planetary gear set with said first member of saidfourth planetary gear set.
 6. The transmission of claim 5, wherein afifth of said five torque transmitting devices is operable forselectively connecting said second member of said third planetary gearset with said first member of said fourth planetary gear set.
 7. Thetransmission defined in claim 1, wherein said first torque-transmittingdevice of said five torque-transmitting devices comprises a brake, andsaid second, third, fourth and fifth of said five torque-transmittingdevices comprise clutches.
 8. The transmission of claim 1, wherein saidfirst, second and third members of said first, second, third and fourthplanetary gear sets comprise a sun gear member, a planet carrierassembly member and a ring gear member, respectively.
 9. Thetransmission of claim 1, wherein said input member is continuouslyinterconnected with said first member of said third planetary gear set,and said output member is continuously interconnected with said thirdmember of said fourth planetary gear set.
 10. A multi-speed transmissioncomprising: an input member; an output member; first, second, third andfourth planetary gear sets each having first, second and third members;said input member being continuously interconnected with said firstmember of said third planetary gear set, and said output member beingcontinuously interconnected with said third member of said fourthplanetary gear set; a first interconnecting member continuouslyconnecting said third member of the first planetary gear set with thefirst member of the second planetary gear set, the third member of thethird planetary gear set and the second member of the fourth planetarygear set; a second interconnecting member continuously connecting saidsecond member of the first planetary gear set with the second member ofthe second planetary gear set; said first member of said first planetarygear set being continuously connected with a stationary member; a firsttorque-transmitting device selectively connecting said second member ofsaid third planetary gear set with said stationary member; a secondtorque-transmitting device selectively connecting said second member ofsaid first planetary gear set with said first member of said thirdplanetary gear set; a third torque-transmitting device selectivelyconnecting said third member of said second planetary gear set with saidfirst member of said fourth planetary gear set; a fourthtorque-transmitting device selectively connecting said first member ofsaid third planetary gear set with said first member of said fourthplanetary gear set; a fifth torque-transmitting device selectivelyconnecting said second member of said third planetary gear set with saidfirst member of said fourth planetary gear set; and said fivetorque-transmitting devices being engaged in combinations of two toestablish at least eight forward speed ratios and at least one reversespeed ratio between said input member and said output member.
 11. Amulti-speed transmission comprising: an input member; an output member;first, second, third and fourth planetary gear sets each having a sungear member, planet carrier assembly member and ring gear member; saidinput member being continuously interconnected with said sun gear memberof said third planetary gear set; said output member being continuouslyinterconnected with said ring gear member of said fourth planetary gearset; a first interconnecting member continuously connecting said ringgear member of said first planetary gear set with said sun gear memberof said second planetary gear set, said ring gear member of said thirdplanetary gear set and said planet carrier assembly member of saidfourth planetary gear set; a second interconnecting member continuouslyconnecting said planet carrier assembly member of said first planetarygear set with said planet carrier assembly member of said secondplanetary gear set; said sun gear member of said first planetary gearset being continuously connected with a stationary member; a firsttorque-transmitting device selectively connecting said planet carrierassembly member of said third planetary gear set with said stationarymember; a second torque-transmitting device selectively connecting saidplanet carrier assembly member of said first planetary gear set withsaid sun gear member of said third planetary gear set; a thirdtorque-transmitting device selectively connecting said ring gear memberof said second planetary gear set with said sun gear member of saidfourth planetary gear set; a fourth torque-transmitting deviceselectively connecting said sun gear member of said third planetary gearset with said sun gear member of said fourth planetary gear set; a fifthtorque-transmitting device selectively connecting said planet carrierassembly member of said third planetary gear set with said sun gearmember of said fourth planetary gear set; and said torque-transmittingmechanisms being engaged in combinations of two to establish at leasteight forward speed ratios and at least one reverse speed ratio betweensaid input member and said output member.